Constitutive Modeling of Sn/Ag and Sn/Ag/Cu Solder Alloys

In this paper, we report some results from a recent study on developing constitutive laws suitable for Sn/Ag and Sn/Ag/Cu based solder materials. Extensive thermomechanical testing has been conducted on these lead-free solder alloys under various temperature (-55C-150C) and strain rate (10-7/s-10-1/s), subjected to both monotonic and cyclic loading. The experimental data are then used to develop a viscoplastic constitutive model to describe the thermomechanical behavior. In addition, a neural network based computational tool has been developed and trained. The tool can be used to extract the various parameters in the constitutive model based on the experimental data. The validity and accuracy of this tool have been verified by using the Anand model on Sn/Pb eutectic solder alloy. Once trained, the tool is capable of extracting all 11 parameters in the Anand model using the experimentally obtained stress-strain curves. These parameters can then be used directly in commercial finite element software such as ANSYS or ABAQUS for solder joint reliability analysis. Using this tool, we have obtained all 11 parameters in the Anand model for Sn/Ag and Sn/Ag/Cu based solder materials